/* e_acosf.c -- float version of e_acos.c.
 * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
 */

/*
 * ====================================================
 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
 *
 * Developed at SunPro, a Sun Microsystems, Inc. business.
 * Permission to use, copy, modify, and distribute this
 * software is freely granted, provided that this notice
 * is preserved.
 * ====================================================
 */


#include "math.h"
#include "float.h"

static const float
one =  1.0000000000e+00, /* 0x3F800000 */
pi =  3.1415925026e+00, /* 0x40490fda */
pio2_hi =  1.5707962513e+00; /* 0x3fc90fda */
static volatile float
pio2_lo =  7.5497894159e-08; /* 0x33a22168 */
static const float
pS0 =  1.6666586697e-01,
pS1 = -4.2743422091e-02,
pS2 = -8.6563630030e-03,
qS1 = -7.0662963390e-01;

float
__ieee754_acosf(float x)
{
    float z,p,q,r,w,s,c,df;
    int hx,ix;
    GET_FLOAT_WORD(hx,x);
    ix = hx&0x7fffffff;
    if(ix>=0x3f800000) {        /* |x| >= 1 */
        if(ix==0x3f800000) {    /* |x| == 1 */
        if(hx>0) return 0.0;    /* acos(1) = 0 */
        else return pi+(float)2.0*pio2_lo;    /* acos(-1)= pi */
        }
        return (x-x)/(x-x);        /* acos(|x|>1) is NaN */
    }
    if(ix<0x3f000000) {    /* |x| < 0.5 */
        if(ix<=0x32800000) return pio2_hi+pio2_lo;/*if|x|<2**-26*/
        z = x*x;
        p = z*(pS0+z*(pS1+z*pS2));
        q = one+z*qS1;
        r = p/q;
        return pio2_hi - (x - (pio2_lo-x*r));
    } else  if (hx<0) {        /* x < -0.5 */
        z = (one+x)*(float)0.5;
        p = z*(pS0+z*(pS1+z*pS2));
        q = one+z*qS1;
        s = sqrtf(z);
        r = p/q;
        w = r*s-pio2_lo;
        return pi - (float)2.0*(s+w);
    } else {            /* x > 0.5 */
        int idf;
        z = (one-x)*(float)0.5;
        s = sqrtf(z);
        df = s;
        GET_FLOAT_WORD(idf,df);
        SET_FLOAT_WORD(df,idf&0xfffff000);
        c  = (z-df*df)/(s+df);
        p = z*(pS0+z*(pS1+z*pS2));
        q = one+z*qS1;
        r = p/q;
        w = r*s+c;
        return (float)2.0*(df+w);
    }
}

float acosf(float  x)
{
    return __ieee754_acosf(x);
}
